The invention relates to manufacturing containers, and in particular to an apparatus and method for contouring a stable bottom for cartons or boxes such as paperboard cartons used for holding liquids, powders and the like, and to containers so contoured.
An example of one common and useful type of container is the paperboard carton having a square cross-section and a gabled top. Examples of such cartons include the everyday milk carton. In recent years, these cartons have been used for numerous other products, including, for example, foods, beverages and detergents. These cartons are typically coated or laminated with a heat-sealable plastic or other suitable material, which is used by manufacturers to seal the cartons.
The bottoms of such paperboard cartons, as well as other types of paperboard or cardboard containers, often are uneven, rather than perfectly flat, making them unstable. That is, rather than standing perfectly upright, the carton rests in a slightly tilted position when placed in the upright position on a flat surface. Furthermore, the carton may rock to a different tilted position if bumped or moved. This rocking and tilting is undesirable to consumers, wholesalers, transporters, grocers and other merchants and distributors of goods packaged in such cartons. This instability typically results from a natural bulge in the carton bottom due to pressure exerted by the product inside and/or discontinuities on the bottom exterior surface formed by overlapping, folded layers within the carton bottom.
Currently, there are several methods to minimize the effects of the problem of instability caused by the bulge.
A carton disclosed in Ljungstrom, U.S. Pat. No. 5,474,232, issued in 1995, provides a concave carton bottom having an arcuate cross-section such that the carton rests on the bottom end of each of two opposing side walls. Col. 7, lines 10-12. This method, however, has the disadvantage that it requires a specially designed carton blank having curved, rather than straight, side creases. Most current carton forming machines are designed to operate with certain standard carton blanks. It can be expensive and inconvenient to procure non-standard carton blanks. It would be desirable to form a concave carton bottom with standard carton blanks.
A packaging machine disclosed in Kume et al., U.S. Pat. No. 4,838,847 which issued in 1989 provides a carton bottom with a substantially pyramidal recessed central cavity. Col. 3, lines 16-20; col. 3, lines 35-40. This carton bottom is supported by end surfaces on all four sides of the carton. This specific configuration is difficult to form, and increases the likelihood of liquids spilling from the carton during transport. A need exists for a simpler stable carton bottom which does not increase the risk of spillage.
A carton bottom sealer disclosed in Mills et al., U.S. Pat. No. 5,482,204 which issued in 1996 provides a carton bottom with a lenticular profilexe2x80x94i.e., a xe2x80x9cconcave, stepped pyramid formed into multiple tiers of lapped layersxe2x80x9d as the profile of the carton bottom. Col. 1, lines 57-58. This carton bottom is formed from a standard carton blank and is intended to be more stable than a traditional carton bottom. However, the structure of the foregoing carton bottom has the disadvantage of being complicated.
Another effort to provide a stable bottom for a carton is described in Fujikawa et al., U.S. Pat. No. 5,222,667 issued in 1993. The ""667 patent discloses forming a recess of inverted V-shaped cross section extending across the bottom closure through the center thereof, so that the recess diminishes the bulge of the bottom closure. The recess has a width approximately equal to the width of the striplike region (31 in FIG. 5 of the Fujikawa et al. patent) having four thicknesses of the container blank. See FIG. 5; col. 3, lines 30-37; col. 2, lines 50-56. Similarly, NiMCO Corporation of Crystal Lake, Ill., had previously provided packaging machines for making cartons having a bottom configuration of the type illustrated in FIG. 1A. In the prior art NiMCO container, the width of the recess also was limited to approximately the width of the center region having four overlapping layers, and the recess did not include the regions where there are fewer than four overlapping layers (i.e., on either side of the four-layer center region).
However, none of the foregoing bottom configurations satisfactorily solve the problem of instability resulting from a bulge in the carton bottom. Accordingly, there is a need for a more stable carton bottom than was provided by the prior art carton bottom configurations.
A need exists for an apparatus and method of forming a stable carton bottom from a standard carton blank which can be used with current carton forming machines. A need also exists for a carton bottom which is inexpensive to produce in current carton forming machines. Additionally, a need exists for providing a stable carton bottom on cartons with other than rectangular side panels, e.g., tapered cartons.
In accordance with the present invention, it has been discovered that forming the carton bottom so that selected regions of the carton bottom exterior surface extend below the surface of another region (i.e., a recessed region) of the carton bottom allows such selected regions to function as legs, thereby providing a more stable bottom structure than prior art methods. This is achieved by making the width of the recessed region wider than in certain of the prior art methods. In the preferred embodiment, the recessed region encompasses substantially the entire center portion of the bottom panel having the maximum number of overlapping layers as well as a substantial portion on either side of such center portion where there are fewer than the maximum number of overlapping layers. Providing such a wider recessed portion results in a marked improvement in carton stability over prior art methods, which had either a narrow center recess or which required either specially configured carton blanks or more complicated carton bottom configurations than the present invention.
In accordance with yet another aspect of the present invention, a stable carton with carton legs is formed from a standard carton blank. Because the present invention may be used with, among other things, a standard carton blank, current carton forming machines may be readily adapted to use the present invention.
Additionally, a standard carton blank is often less expensive and more readily available than a specially designed carton blank.
In accordance with yet another aspect of the present invention, a carton bottom is formed with a simple mechanism which can be readily incorporated into current carton forming machines. The present invention relates to a novel seal plate and mandrel pad which contour the carton bottom.
The present invention is advantageous because it easily and inexpensively can be adapted to and integrated into existing carton forming machines. For example, the sealing horn 22 and mandrel pad 40 of U.S. Pat. No. 3,971,300 or the pressure pad 118 and mandrel 120 of Hyduk, U.S. Pat. No. 5,135,463, as well as the horn and mandrel pad of other existing carton forming machines could be modified to incorporate the present invention.
In accordance with the present invention, a carton bottom is formed with improved stability. This improved stability is desirable for transportation, storage and display of the cartons to customers.